The present invention relates to a method and a device for protecting against a press overload to prevent damage to a press machine when the press machine receives an overload.
In a press machine such as a punch press or the like, when a striker strikes a punch to cause that punch to descend, if the punch is unable to descend, for example, as the result of a galling phenomenon of a punch and a die, an excessive load is produced. Conventionally, the following types of devices are known as press overload prevention devices for preventing damage to the punch or the striker or the like.
Specifically, for a mechanical press, Japanese Examined Patent Publication (KOKOKU) 52-27393 discloses a structure in which a shear plate is set directly in the striker so that, when an excessive load occurs, this shear plate is punched by the striker, and the punch is unable to perform the punching operation.
In addition, the following methods are known for use with hydraulic press, or a mechanical press with a cylinder built into the ram.
(A) A safety accumulator or a safety valve is provided on the pressurized side of the circuit. PA0 (B) An emergency halt is applied to the impacting operation when the generation of excessive hydraulic pressure is detected on the pressurized side of the circuit. PA0 (C) The above two methods are combined.
The method by which a shear plate is directly set in the striker is not suitable with respect to the structure of a hydraulic press. In addition, the method by which a safety accumulator or a safety valve is provided on the pressurized side of the circuit, or the method by which an emergency halt is applied to the impacting operation when the generation of excessive hydraulic pressure is detected on the pressurized side of the circuit, requires a rather large amount of time for the application of hydraulic pressure to the accumulator, the release of hydraulic pressure by the safety valve, or the application of the emergency halt to the impacting operation. Accordingly, the prevention of damage to the striker, punch or the like cannot always be said to be adequate. Furthermore, because these devices such as a safety valve or the like must operate when a high pressure occurs from excessive hydraulic pressure, they must have a large capacity and are therefore high-priced devices.